This invention relates to a power transmission chain belt and, in detail, to a rockerjoint for a continuously variable transmission (CVT) chain belt having stepped pins that are press fit in the center of the guide links.
A link plate chain, as disclosed in Laid-Open Patent H11-241753, is used conventionally as a power transmission chain belt. As shown in FIGS. 1 and 3 and in column 6, lines 18-33 of the said patent publication, in this link plate chain, interleaved chain link plates 1 and outside link plates 2 are connected pivotally by a pair of oscillation pieces (connecting pin) 3, which are joint members.
As shown in FIG. 3 of the said publication, a pair of oscillation pieces 3 have the same length in this link plate chain and each of oscillation pieces 3 contacts with a conical pulley for power transmission by the frictional force between the said pulley and oscillation piece.
When a chain is wound on the pulley, oscillation pieces 3 roll on an oscillation surface (rolling surface) 6, and, at that time, a pair of oscillation pieces 3 rotate in the opposite direction inside a pin aperture 4. Therefore, power is lost because of the slipping that occurs between the end face of the oscillation piece and the pulley.
Recently, a chain belt power transmission device has been used under high load and, at the same time, it is required to have high wear-resistance. However, when a conventional chain belt is used under heavy load, very high contact surface pressure is generated on the convex-to-convex contact surface of the connecting pin and, as a result, pitting wear occurs on the rolling surface of the connecting pin, so that the conventional chain belt cannot sufficiently satisfy the requirement for wear-resistance.
The radius of curvature of the rolling surface of the connecting pin can decrease the contact surface pressure among connecting pins but a larger radius of curvature of the rolling surface impedes bending of link plates and bendability of the entire chain belt and, as a result, its winding on a small-diameter pulley becomes more difficult. Therefore, increasing the radius of curvature of the rolling surface is limited from the viewpoint of ensuring bendability of the entire chain belt.
This invention addresses such a conventional problem and it offers a power transmission chain belt which can reduce the surface pressure acting on the connection pin while maintaining bendability of the entire chain belt.
Construction of the connecting pin of the present invention is detailed below with the aid of FIG. 3. In the figure, inner links 2a, 2b, put together at a right angle to the paper surface, are bent to each other. Incidentally, in such a case, the bending angle is given as xcex1. Connecting pin 3 that pivotally supports said inner links 2a, 2b is inserted in pin aperture 22 of the said inner links 2a, 2b. 
Connecting pin 3 is composed of center pin 31 arranged at the center of pin aperture 22 and a pair of rocker pins arranged on both sides of the center pin. Both side faces 31a of center pin 31 are convex curved and a convex curved face 32a, which contacts both side faces 31a of center pin 31, is formed in rocker pin 32.
Now, in a conventional link plate chain, rolling contact at angle a on the rolling surface of a pair of connecting pins (oscillation pieces) is necessary to produce bending angle xcex1.
Whereas, in the present invention, as shown in FIG. 3, rolling contact at angle xcex1/2 of each rocker pin 32 suffices to produce a bending angle xcex1 between adjacent inner links 2a, 2b, because rocker pins 32 are arranged on both sides of center pin 31. Therefore, rolling contact of a rocker pin at one half of the necessary angle of the rolling contact suffices for the present invention so that the radius of curvature of each pin can be increased by that much and thereby the surface pressure of the contact surface of each pin can be reduced and wear-resistance improved.
In the present invention, both end faces of the center pin contact with the pulley""s friction surface so that, when a chain is wound on a pulley, the end face of the center pin only contacts the pulley""s friction surface and the end face of the rocker pin does not contact. Thereby, generation of slippage between the pin""s end face and the pulley is prevented, loss of power transmission is reduced and heat generation from the operation is reduced.
The preferred shape of the center pin cross-section is approximately a Japanese drum shape, or a general ellipse. This is a shape in which the centers of both side faces are convex curved outward. Concave or convex curved faces are formed on the opposing faces of the convex curved face of the rocker pin.
Steps are formed at the tip of the center pin and the stepped part is press-fitted into the pin aperture of the outer link plate. In such case, detachment of the center pin from the link plate is prevented assuredly.